Electrical signals passing across an automotive paint booth barrier may require conditioning by intrinsically safe barrier ISB circuitry for electrical power limiting in the booth. When signal accuracy is critical, transformer isolated ISBs are conventionally required. Transformer isolated ISBs use well-known switching technology to transfer signals across the barrier. The switching technology injects significant noise into the signals passing across the ISB. Heavy filtering is required to reduce the noise, for example using a lag filter process with a long filter time constant. The long filter time constant of such a filter process adds significant time lag to the signal, reducing signal accuracy during transients. Such a filtered signal may be used only when steady state signal information is sufficient. In applications requiring signal accuracy during transient conditions, such as conditions characterized by a substantial time rate of change in the signal magnitude, such heavy filtering is unacceptable. Therefore, transformer-based ISBs, or indeed any barrier circuitry that significantly corrupts signals passing across booth barriers is unacceptable in such applications.
It has been proposed to provide a potentiometer-based paint flow volume feedback signal in a paint flow control system, wherein a potentiometer wiper position varies with variation in a paint control volume, and wherein the potentiometer output signal indicating the wiper position at any time during a paint control process is passed across a paint booth barrier to a paint flow controller. The feedback signal may then be used to dynamically vary control parameters for closed-loop paint flow control. If precision in paint flow control is desired, the feedback signal must accurately indicate paint flow volume throughout the control process. Traditional guidelines suggest that such a precision feedback signal must pass across a transformer based ISB. However, the dynamic control of such systems requires a responsive potentiometer wiper position indication, which preempts use of the heavy filtering required with the transformer based ISBs.
Accordingly, what is needed is intrinsically safe barrier circuitry having high accuracy and minimum signal lag across a paint booth barrier.